Hello,
I just did a "quick and dirty" comparison of my Iskra-2 with my Weltax (3,5/75 CZJ Tessar). At f/8 the Iskra is still a bit soft in the corners, not so the Tessar. And you can get a Weltax for under 20 Euro in Germany.
OK - the Weltax is missing the Selenium Meter and the Rangefinder - but you won't have any frame spacing problems, unless you are able to count numbers in the little Window at the back ;-)
Regards,
Andreas